KR20000023979A - Circuit for starting of induction motor - Google Patents

Abstract

PURPOSE: A drive circuit of an induction motor is provided to prevent a power loss owing to a power control device by applying current to the motor through the power control device after completing to drive the motor. CONSTITUTION: A drive circuit of an induction motor comprises a synchronous signal generating circuit(200) which converts 220V into 12V at an input of an R-phase of a three-phase alternating current power and rectifies the voltage of 12V to output a synchronous signal. An operation panel(300) has a plurality of function buttons so that an operator selects a driving mode of an induction motor(1). A programmable logic device(PLD)(400) outputs a phase control signal when an automatic driving mode is selected by the operation panel(300). The phase control signal is to increase a voltage, which is supplied to a power control device in an initial driven time of the motor by the synchronous signal with the passage of time, as a time elapses. A silicon controlled rectifier driving circuit(500) turns on and off the power control device according to the phase control signal, and turns on the power control device before a magnetic contactor(3) is opened at a stop of the motor(1). A magnetic contact control circuit(600), if the initial driven time elapses, controls so that an alternating current power of each phase is supplied to the motor through the magnetic contactor driven by the control signal.

Description

CIRCUIT FOR STARTING OF INDUCTION MOTOR

The present invention relates to a starting circuit of an induction motor, and more particularly, to generate a synchronous signal in the form of a pulse with a three-phase AC power source, by using the silicon controlled rectifier to control the silicon controlled rectifier during the initial start-up It supplies power to an induction motor, and supplies power to a magnetic contactor during operation when the operation is completed, and controls a magnetic contactor in an emergency so that a three-phase AC power is directly applied to the induction motor. .

In general, induction motors are AC motors, which are relatively simple in structure, easy to handle, and inexpensive, and have been applied to various machines over a wide range of capacities. These induction motors are of single phase and three phase.

A three-phase induction motor is a three-phase coil wound around a field iron core. When a current flows through a three-phase coil, a rotating magnetic field is formed to rotate the armature by the interaction of induction power generated in the armature coil. It is widely used in industrial electrical equipment such as brake and power tester.

Such a motor generates an initial current, that is, starting torque of 400% of the total load and starting current of 600-700% when starting current is input.

Starting torque causes wear and damage of the induction motor and the gears, belts, and bearings attached thereto, and the starting current causes a voltage drop to increase the facility capacity.

Thus, a starting circuit for suppressing the starting current of such a medium-large induction motor of 15 horsepower or more has been developed.

A conventional induction motor starting circuit is provided with a power control element (Silicon Controlled Rectifier (SCR), 3-pole AC switch (Triac)) between a three-phase AC power source and an induction motor, and induction is turned on and off. The electric current was put into the electric motor.

However, the starter circuit of the induction motor using such a conventional power control element generates a power loss of the power control element by applying a current to the induction motor through the power control element, and when the induction motor is operated for a long time, As a result, there is a problem that the power control element is burned out and short-circuited during operation.

In addition, there is another problem that additional costs are generated by forming another current supply routine to apply current to the induction motor when an abnormality of the power control element occurs.

In addition, there is another problem that the volume of the starter circuit itself becomes relatively large due to the use of a bulky heat sink to dissipate heat generated by the power control device to the outside.

In addition, there is another problem that a radio wave is generated in a system in which noise is generated from a power control element.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and induces an induction motor by applying power to the power control element only at the initial start or stop of the induction motor, and in parallel with the power control element when the induction motor is completed. Connect the connected magnetic contactor to apply current to the induction motor through the power control element to prevent power loss from the power control element, and apply only the initial current to the power control element so that the power control element can To prevent them from happening.

In addition, another object of the present invention is to prevent the additional installation of unnecessary other current supply routine by supplying a current to the magnetic contactor in the event of an abnormality of the power control element.

In addition, another object of the present invention is to not use the power control element for a long time during normal operation to generate a large amount of heat in the power control element can be relatively reduced in the size of the heat sink to minimize the volume of the starting circuit have.

In addition, another object of the present invention is to prevent the generation of radio interference in the system by preventing the generation of noise from the power control element.

1 is a block diagram schematically showing the configuration of a starting circuit of an induction motor according to the present invention;

2 is a timing diagram of a synchronization signal generation circuit of FIG.

3 is a circuit diagram showing in detail the configuration of the start signal and stop signal generation circuit of the PLD in FIG.

4 is a block circuit diagram showing in detail the configuration of the control sequence circuit of the PLD in FIG.

5 is a timing diagram of the control sequence circuit of FIG.

6 is a circuit diagram showing in detail the configuration of the phase control circuit of the PLD in FIG.

7 is a timing diagram showing an output waveform of the phase control circuit of FIG.

FIG. 8 is a circuit diagram showing in detail the configuration of the silicon control rectifier driving circuit of FIG.

9 is a block circuit diagram showing in detail the configuration of the emergency drive circuit of FIG.

10 is a timing diagram illustrating an output waveform of FIG. 9.

<Explanation of symbols for main parts of the drawings>

1: induction motor 2: silicon controlled rectifier

3: magnetic contactor 100: starting circuit

200: synchronization signal generating circuit 300: operation panel

400: PLD 500: silicon controlled rectifier driving circuit

600: magnetic contactor control circuit 700: emergency drive circuit

Features of the present invention for achieving the above objects,

In a starting circuit of an induction motor for starting an induction motor by using a plurality of power control elements connected to each phase of a three-phase AC power supply and a plurality of magnetic contactors connected in parallel to the respective power control elements,

A synchronization signal generation circuit for converting each phase of the input three-phase AC power source into a pulse current, and thereby generating a pulse type synchronization signal;

When the automatic operation mode is selected by the user's operation, the voltage supplied to the power control element increases as time passes by the synchronization signal of the synchronization signal generation circuit within the initial starting time of the induction motor. A PLD for outputting a phase control signal

The power control device is sequentially turned on and off according to a phase control signal supplied from the PLD, and the power control device is turned on before opening the magnetic contactor when the induction motor is stopped, thereby A power control element driving circuit for opening the contact of the magnetic contactor without potential;

A magnetic contactor control circuit for controlling the AC power to be supplied to the induction motor through the magnetic contactor by operating the magnetic contactor according to the control signal of the PLD when the initial starting time elapses;

When the inching operation mode is selected by the user's operation, an inching signal is output to the magnetic contactor control circuit so that the terminals of the magnetic contactor are repeatedly contacted and opened. And an emergency driving circuit for outputting a direct signal to the control circuit to contact terminals of the respective magnetic contactors.

Here, the PLD is

A start signal and a stop signal generation circuit for generating and outputting a start signal and a stop signal when the automatic driving mode is selected by a user's operation;

A clock signal generation circuit for generating and outputting a clock signal required by the PLD;

A control sequence circuit for outputting a control signal according to a control timing of a system by counting a clock signal supplied from the clock signal generation circuit when an output signal is supplied from the start signal and the stop signal generation circuit;

And a phase control circuit for raising the voltage supplied to each of the power control elements over time according to a control signal supplied from the control sequence circuit.

Here also the phase control circuit,

An up counter which is reset according to the synchronization signal of each phase input from the synchronization signal generation circuit and up-counts the time after the synchronization signal input of each phase for a predetermined time;

A down counter which is reset by a start signal supplied from the start signal and the stop signal generation circuit to start down counting;

And a comparison unit comparing the up counting signal of the up counter and the down counting signal of the down counter to adjust a supply time of a voltage supplied to the power control element according to a comparison value.

Here, the emergency drive circuit,

A first flip-flop that is set when the inching operation mode is selected and outputs a predetermined signal;

A first timer that is triggered according to an output signal supplied from the first flip-flop and outputs a high signal;

A first time constant circuit comprising a variable resistor and a condenser to delay the trigger time of the first timer by a time constant;

A second timer triggered according to a signal output from the first timer,

A second time constant circuit comprising a variable resistor and a condenser to delay the trigger time of the second timer by a time constant;

A third timer triggered according to a signal output from the second timer,

A third time constant circuit comprising a variable resistor and a condenser to delay the trigger time of the third timer by a time constant;

A fourth timer triggered according to the signal output from the third timer,

A fourth time constant circuit comprising a variable resistor and a condenser to delay the trigger time of the fourth timer by a time constant;

A second flip-flop latched by the high signal supplied from the fourth timer and outputting a high signal;

The first timer, the third timer and the second flip-flop are respectively connected in parallel, and when a high signal is output from the first timer, the third timer and the second flip-flop, And a diode for converting an output signal of the first timer, the third timer, and the second flip-flop into an inching signal.

Hereinafter, the configuration and operation of the starting circuit of the induction motor according to the present invention will be described in detail with reference to FIGS. 1 to 10.

1 is a block diagram schematically showing the configuration of a starting circuit of an induction motor according to the present invention.

Referring to FIG. 1, the starting circuit 100 of the induction motor according to the present invention includes a synchronization signal generating circuit 200, an operation panel 300, a programmable logic device (PLD) 400, and a silicon controlled rectifier driving circuit. The furnace 500, the magnetic contactor control circuit 600 and the emergency drive circuit 700 is composed of.

When the R phase (S phase, T phase) of the 220 V three-phase (RS T) AC power is input, the synchronous signal generation circuit 200 changes the 220 V power to a voltage of 12 V necessary for the system, and rectifies the voltage of 12 V. As shown in FIG. 2, a pulse signal, that is, a synchronous signal, is output at twice the frequency of the input power source as compared with the pulse voltage and the constant voltage supplied from the outside.

The operation panel 300 is provided with a plurality of function buttons (not shown) so that an operator can select an operation mode (automatic operation mode, inching mode, direct operation mode) of the induction motor 1.

The PLD 400 includes a start signal and a stop signal generation circuit 410, a clock signal generation circuit 420, a control sequence circuit 430, and a phase control circuit 440.

As shown in FIG. 3, the start signal and stop signal generation circuit 410 includes a first logical AND1, a first flip-flop FF1, a first logical negative NOT1, and a second logical product. AND2, a second flip-flop FF2, and a second logic negative NOT2.

The first logical ANDAND outputs a high signal when a high signal is output from a start key (not shown) among the function keys of the operation panel 300. The first flip-flop FF1 outputs a first logical AND1. When the high signal is supplied from the signal, the high signal, that is, the start signal is output, and then the inverted signal is input to the D port through the first logic negative NOT1, and the low signal is input to the C port at the first logical AND1. Is latched. Thus, the low signal output from the first flip-flop FF1 is output to the control sequence circuit 430 of the PLD 400. The second logical AND2 outputs a high signal from a stop key (not shown) among the function keys of the operation panel 300, and the second flip-flop FF2 supplies a high signal from the second logical AND2. If a high signal is output, that is, a stop signal is output and latched. The second logic negative NOT2 inverts the signal output from the second flip-flop FF2 and latches the output signal of the D port of the second flip-flop FF2 by the output signal of the second logical AND AND2. Keep it.

The clock signal generation circuit 420 starts oscillation according to a constant voltage Vcc input from the outside, generates a first oscillation frequency and a second oscillation frequency, divides the first oscillation frequency, and generates a clock signal. The oscillation frequency is supplied to the phase control circuit 440 of the PLD 400.

As shown in FIG. 4, the control sequence circuit 430 repeatedly turns on and off the silicon control rectifier 2 when the induction motor 1 is started in the autonomous driving mode. Start the magnetic contactor (3) and then turn off the silicon-controlled rectifier (2). When the induction motor 1 is stopped, the first counter 431 and the decoder 432 turn the silicon controlled rectifier 2 on, then the magnetic contactor 3 off, and then the silicon controlled rectifier 2 off. ), The first logical sum OR1, the second logical sum OR2, the third logical sum OR3, the exclusive logical sum EX-OR, the third logical negation NOT3, and the third logical sum AND3).

Referring to the operation of the control sequence circuit 430, when a clock signal is supplied from the clock signal generation circuit 420, the first counter 431 starts counting the supply time, and the decoder 432 at the first counter 431 The signal is outputted according to the control timing by using the counting signal supplied from the ().

When the output signal of the start key of the function keys of the operation panel 300 is input in the autonomous operation mode, a low signal is output from the first flip-flop FF1 of the start signal and the stop signal generating circuit 410, and thus the first counter. Operation 431 is cleared and the high signals are sequentially output from the output ports d1 to d15 of the decoder 432.

In more detail, the second counter 441 of the phase control circuit 440 is operated by outputting a set pulse signal for controlling the silicon control rectifier 2 at d1 of the decoder 432. A control signal is output so that a signal for setting a phase control section of the silicon control rectifier 2 is output as shown in FIG. 5 in the first logical sum OR1 connected to d3 and d4 at d2 of the decoder 432.

At the same time, the decoder 432 enters a start-end signal for notifying that the phase control section, which is the initial start time of the silicon control rectifier 2, is terminated through the exclusive logical sum EX-OR. That is, when the output of d3 of the decoder 432 is a high signal or the counter value drops to " 0 " from the down counter 442 of the phase control circuit 440, the output of the exclusive logical sum (EX-OR) is low. As a signal, a low signal is output from the third logical product AND3.

Also, since the third logic OR3 outputs a low signal before the high signal is output from the second flip-flop FF2 of the start signal and the stop signal generator 410, the first counter 431 temporarily stops counting. As a result, the output of the decoder 432 is maintained at d3 so that the value of the down counter 442 of the phase control circuit 440 drops to " 0 " so that the down counter 442 generates a counter end signal (0-CONT). It waits for output. Therefore, during the set initial startup time, the silicon controlled rectifier 2 is kept in the phase control state.

Therefore, if the counter end signal is output from the down counter 442 after the initial start time (about 20 to 30 seconds) has elapsed, the phase control circuit 440 outputs a high signal to the exclusive logical sum (EX-OR). (EX-OR) outputs a high signal, and when the high signal is output from the exclusive OR, the third logical AND3 is high because the high signal is not yet output at d6 of the decoder 432. Output the signal. Then, since the third logical OR OR also outputs a high signal, the first counter 431 resumes counting, and the high signal is output at d4 of the decoder 432 to turn on the magnetic contactor 3. When the high signal is output at d6 of the decoder 432, the signal inverted by the third logic negative NOT3 is input to the third logical AND3 to hold the first counter 431 again.

As the high signal is continuously output from the second logic OR OR connected to d4, d5, d6, and d7, in which the output signal of the decoder 432 is sequentially output, the induction motor (3) is operated through the magnetic contactor (3) during the routine operation time. Subsequently to 1), a three-phase AC power supply is applied.

In this state, when the stop signal, ie, the high signal, is input to the third logical sum OR3 through the second flip-flop FF2 of the start signal and the stop signal generator 410, the first counter 431 starts counting again. The high signal is output at d7 of the decoder 432 to turn on the silicon controlled rectifier 2.

Then, a high signal is output at d8 of the decoder 432 to turn off the magnetic contactor 3, and then a stop-end signal of d9 of the decoder 432 is output to produce a start signal and a stop signal generating circuit. The first flip flop FF1 and the second flip flop FF2 of 410 are reset. The reason for turning off the magnetic contactor 3 while the silicon controlled rectifier 2 is turned on is that the magnetic contactor 3 connected in parallel to the silicon controlled rectifier 2 when the silicon controlled rectifier 2 is turned on. Since the same potential is applied to both of the contacts, the arc is prevented from occurring when the magnetic contactor 3 is turned off.

As shown in FIG. 6, the phase control circuit 440 includes a second counter 441, a down counter 442, and a comparator 443.

The second counter 441 is reset according to the synchronization signal of each phase input from the synchronization signal generation circuit 200, and counts up the time after the synchronization signal input of each phase for a predetermined time, but is counted at full scale. In case it is held at full scale. The down counter 442 is reset by the start signal supplied from the start signal and the stop signal generation circuit 410, and is set down by the second oscillation frequency supplied from the clock signal generation circuit 420 (initial start time). ) Counts down and outputs a counting end signal when the down counting ends. The comparator 443 compares the up counting signal of the second counter 441 and the down counting signal of the down counter 442 and outputs a comparison result. That is, the comparator 443 generates an output signal in a section in which the up counting value of the second counter 441 is greater than the down counting value of the down counter 442, thereby decreasing the counting value of the down counter 442. As shown in FIG. 7, the output pulse width increases with time, and the turn-on time of the silicon controlled rectifier 2 is increased, so that the voltage applied to the induction motor 1 gradually rises, thereby initiating the initial stage of the induction motor 1. A maneuver is made. Here, a logic circuit is provided inside the comparator 443.

As illustrated in FIG. 8, the silicon controlled rectifier driving circuit 500 uses an optical coupler 510 to prevent noise from penetrating into the circuit, and converts a signal supplied from the optical combiner 510 into an amplifying transistor TR1. After amplifying at, the signal supplied from the amplifying transistor TR1 is converted into a pulse-shaped signal by the pulse transformer T1 and output to the silicon-controlled rectifier 2. In the drawings, reference numerals D1 and D2 denote reverse voltage preventing diodes, and R1 and R2 denote potential generating resistors.

As shown in FIG. 9, the emergency driving circuit 700 is set when the inching operation mode signal is supplied from the operation panel 300 to output a predetermined signal, and the third flip flop FF3. A first timer 710 triggered according to an output signal supplied from the flop FF3 and outputting a high signal, and a variable resistor VR1 and a condenser C1 to delay the trigger time of the first timer 710 by a time constant. Variable resistance to delay the trigger time of the first time constant circuit 720, the second timer 730 triggered according to the signal output from the first timer 710, and the second timer 730 by a time constant Time constants for the trigger time of the second time constant circuit 740 including the VR2 and the condenser C2, the third timer 750 triggered according to the signal output from the second timer 730, and the third timer 750. With variable resistance VR3 and capacitor C3 to delay by The third time constant circuit 760, the fourth timer 770 triggered according to a signal output from the third timer 750, and the trigger time of the fourth timer 770 is delayed by a time constant. A fourth time constant circuit 780 consisting of a resistor VR4 and a capacitor C4, a fourth flip-flop FF4 latched by a high signal supplied from the fourth timer 770 to output a high signal, and a first timer ( 710, a third timer 750, and a fourth flip-flop FF4 are connected in parallel, respectively, and a high signal is generated at the first timer 710, the third timer 750, and the fourth flip-flop FF4. When output, diodes D4, D5, and D8 are turned on to output inching signals. In the drawing, reference numerals D6 and D7 denote diodes for preventing reverse voltage.

The operation of the emergency driving circuit will be described in detail with reference to FIGS. 9 to 10. When the inching operation mode signal is supplied from the operation panel 300 during the operation mode, the third flip of the start signal and the stop signal generation circuit 410 is performed. The flop FF3 is set and a high signal is output to trigger the first timer 710, and at the same time, the first timer 710, the second timer 730, the third timer 750, and the fourth timer ( 770 is reset to initialize.

When the first timer 710 is triggered, a high signal is output from the output side thereof, which is changed into a low signal after a predetermined time delay by the first time constant circuit 720 to trigger the second timer 730. As such, when the third timer 750 and the fourth timer 770 are sequentially triggered, the fourth flip-flop FF4 is set by the output signal of the fourth timer 770 to drive the magnetic contactor 3. Is output as shown in FIG. If the stop signal is input, the third flip-flop FF3 is reset to reset the first to fourth timers 710, 730, 750, and 770 and the fourth flip-flop FF4.

In this state, when the direct operation mode signal is output from the operation panel 300 in the operation mode, the fourth flip-flop FF4 is set and a signal for driving the magnetic contactor 3 is output.

Therefore, according to the configuration described above, the induction motor is started by applying power to the silicon controlled rectifier only at the initial start or stop of the induction motor, and when the induction motor is driven, the silicon control rectifier is connected by connecting a magnetic contactor connected in parallel with the silicon controlled rectifier. The current is applied to the induction motor to prevent the loss of power in the silicon controlled rectifier, and only the current is applied to the silicon controlled rectifier only at the initial start and stop of the induction motor. To prevent them.

As described above, according to the starting circuit of the induction motor according to the present invention, the following advantages occur.

First, the induction motor is started by applying power to the silicon controlled rectifier only at the initial start or stop of the induction motor, and when the induction motor is driven, the magnetic contactor connected in parallel with the silicon controlled rectifier is connected to the induction motor through the silicon controlled rectifier. Applying a current can prevent power loss in the silicon controlled rectifier.

Secondly, the silicon controlled rectifier applies current only during the initial driving and stopping of the induction motor, and when the induction motor is driven, power is supplied to the induction motor through the magnetic contactor, whereby the silicon controlled rectifier causes burnout and short circuit during operation. Can be prevented.

Third, supplying current to the magnetic contactor in the event of a failure of the silicon controlled rectifier prevents the additional installation of other current supply routines.

Fourth, since the silicon controlled rectifier is not used for a long time, much heat is not generated in the silicon controlled rectifier, so that the size of the heat sink can be relatively reduced, thereby minimizing the volume of the starting circuit.

Fifthly, by using an optical coupler in the silicon controlled rectifier drive circuit to electrically separate the silicon controlled rectifier and the circuit, it is possible to prevent noise from being generated in the silicon controlled rectifier, thereby preventing the occurrence of radio interference in the system.

Claims (4)

In a starting circuit of an induction motor for starting an induction motor by using a plurality of power control elements connected to each phase of a three-phase AC power supply and a plurality of magnetic contactors connected in parallel to the respective power control elements, A synchronization signal generation circuit for converting each phase of the input three-phase AC power source into a pulse current, and thereby generating a pulse type synchronization signal; When the automatic operation mode is selected by the user's operation, the voltage supplied to the power control element increases as time passes by the synchronization signal of the synchronization signal generation circuit within the initial starting time of the induction motor. A PLD for outputting a phase control signal The power control device is sequentially turned on and off according to a phase control signal supplied from the PLD, and the power control device is turned on before opening the magnetic contactor when the induction motor is stopped, thereby A power control element driving circuit for opening the contact of the magnetic contactor without potential; A magnetic contactor control circuit for controlling the AC power to be supplied to the induction motor through the magnetic contactor by operating the magnetic contactor according to the control signal of the PLD when the initial starting time elapses; When the inching operation mode is selected by the user's operation, an inching signal is output to the magnetic contactor control circuit so that the terminals of the magnetic contactor are repeatedly contacted and opened, and when the direct operation mode is selected by the user's operation, the magnetic contactor And an emergency driving circuit for outputting a direct signal to a control circuit to contact terminals of the respective magnetic contactors. The method of claim 1, The PLD is, A start signal and a stop signal generation circuit for generating and outputting a start signal and a stop signal when the automatic driving mode is selected by a user's operation; A clock signal generation circuit for generating and outputting a clock signal required by the PLD; A control sequence circuit for outputting a control signal according to a control timing of a system by counting a clock signal supplied from the clock signal generation circuit when an output signal is supplied from the start signal and the stop signal generation circuit; And a phase control circuit for raising a voltage supplied to each of the power control elements with time according to a control signal supplied from the control sequence circuit. The method of claim 2, The phase control circuit, An up counter which is reset according to the synchronization signal of each phase input from the synchronization signal generation circuit and up-counts the time after the synchronization signal input of each phase for a predetermined time; A down counter which is reset by a start signal supplied from the start signal and the stop signal generation circuit to start down counting; And a comparator configured to compare an up counting signal of the up counter and a down counting signal of the down counter to adjust a supply time of a voltage supplied to the power control element according to a comparison value. The method of claim 1, The emergency drive circuit, A first flip-flop which is set when the inching operation mode is selected and outputs a predetermined signal; A first timer that is triggered according to an output signal supplied from the first flip-flop and outputs a high signal; A first time constant circuit comprising a variable resistor and a condenser to delay the trigger time of the first timer by a time constant; A second timer triggered according to a signal output from the first timer, A second time constant circuit comprising a variable resistor and a condenser to delay the trigger time of the second timer by a time constant; A third timer triggered according to a signal output from the second timer, A third time constant circuit comprising a variable resistor and a condenser to delay the trigger time of the third timer by a time constant; A fourth timer triggered according to the signal output from the third timer, A fourth time constant circuit comprising a variable resistor and a condenser to delay the trigger time of the fourth timer by a time constant; A second flip-flop latched by the high signal supplied from the fourth timer and outputting a high signal; The first timer, the third timer and the second flip-flop are respectively connected in parallel, and when a high signal is output from the first timer, the third timer and the second flip-flop, And a diode for converting an output signal of the first timer, the third timer, and the second flip-flop into an inching signal.